Influence of L-leucine and L-alanine on Lrp regulation of foo, coding for F1651, a Pap homologue

Abstract

The foo operon encodes F165 1 fimbriae that belong to the P-regulatory family and are synthesized by septicemic Escherichia coli. Using an Lrp-deficient host and the lrp gene cloned under the arabinose pBAD promoter, we demonstrated that foo was transcribed proportionally to the amount of Lrp synthesized. L-leucine and L-alanine decreased drastically the steady-state transcription of foo and modified phase variation, independently of the presence of FooI. Specific mutations in the C-terminal region of Lrp reduced or abolished the repressive effect of these amino acids, indicating that they modulate F165 1 by affecting Lrp.

FIG. 1.

Schematic representations of fooIB-lacZYA and fooB-lacZYA fusions. (A) Strain FB1001 and derivatives bearing the fooIB-lacZYA fusion, including the fooI gene. (B) Strain FB2001 and derivatives bearing the fooB-lacZYA fusion, without the complete fooI gene. These fusions have been inserted at the attB site into the chromosome of E. coli CT4A by using the λRS45 derivative phages (λMT01 and λMT02). Both transcriptional fusions contained the foo regulatory region, including the two GATC sites. The arrows show the orientation of transcription, and p indicates foo promoters.

FIG. 2.

Influence of Lrp mutations and effects of leucine and alanine at 1.5 mM on the expression of fooBp. (A) fooIB-lacZ derivatives strain FB1002, containing wild-type Lrp (solid lines, black squares), and strain FB1001, deficient in Lrp (dotted line, empty squares). (B) fooB-lacZ derivatives FB2002, containing wild-type Lrp (solid lines, black squares), and FB2001, deficient in Lrp (dotted line, empty squares). The curves obtained in minimal medium without the addition of amino acids are represented by black squares, with the addition of alanine shown by empty triangles and the addition of leucine indicated by an X. The Durnett test was used to compare the effect of different Lrp concentrations on the foo operon (9). MU, Miller units.